Assessing Atrazine

Rhonda Brooks | Jan 01, 2006

While you're applying atrazine in cornfields this spring, the U.S. Environmental Protection Agency (EPA) will be finalizing its review on the cumulative risk of the triazine family of herbicides, of which atrazine is a member. The EPA decision is due tentatively this May.

Atrazine is an integral part of corn production in the U.S. EPA estimates in its latest atrazine review that U.S. farmers would need to spend an additional $28/acre to retain current yield levels if the product wasn't available for weed control.

Duane Martin, herbicide brand manager for Syngenta, says out of the 81.5 million U.S. corn acres, about 62 million are treated with atrazine, which simply underscores the value of the product to agriculture. Atrazine is present in at least 140 different herbicide brands currently on the market.

The good news is that best management practices (BMPs) adopted by farmers during the past decade have helped decrease atrazine levels in water dramatically. In a study by the U.S. Geological Survey, conducted following spring herbicide applications, atrazine levels in 53 Midwestern streams had decreased approximately 47% in the period between 1989 and 1995. Atrazine manufacturing representatives say that levels of atrazine in water continue to decrease, with standard applications involving about 30% less product.

“Most growers used 2.5-4 lbs./acre of active ingredient 15 years ago,” Martin says. “Today, the average rate in the Corn Belt is closer to 1.5-2 lbs./acre.”

Despite the decreased application rates and use of BMPs, levels of atrazine in water that occasionally exceed 3 ppb are unacceptable to many Americans.

In 2003, EPA entered into an agreement with manufacturers to develop and manage a comprehensive monitoring program for those water systems exhibiting high levels of atrazine, beyond the EPA established standards. Martin says Syngenta, along with some other manufacturers, had already been monitoring drinking water levels on a voluntary basis in areas where atrazine is used most.

EPA and manufacturers agreed to develop three aspects to the overall program: monitoring, mitigation and market elimination.

Monitoring simply involves the process of checking at-risk water supplies, most of which are surface water resources, such as reservoirs.

If atrazine exceeds EPA levels of concern, then the manufacturers initiate mitigation. In Region 7, which includes Missouri and Iowa, that has involved bringing together a number of individuals and organizations to develop a set of BMPs, essentially solutions, for the specific problem identified, says Kristie Raymond, EPA regional pesticides and water quality coordinator.

“Our experience in Region 7 has been a collaborative approach to the problem, and it's brought everyone together at the table,” she says. That everyone includes grower groups, manufacturers, Extension specialists and EPA representatives. The group determines the set of BMPs, which farmers can then employ voluntarily.

Smithville Lake, a body of water just north of Kansas City, MO, is one example where the use of BMPs by farmers turned a negative situation into a positive. Two years ago, Smithville Lake was one of several Missouri bodies of water that EPA had listed as “impaired” due to atrazine levels. However, the use of BMPs such as reduced application rates, soil incorporation, split applications and careful application timing to minimize runoff helped improve water quality and contributed to EPA removing Smithville Lake from the impaired category.

In some cases, however, where impaired bodies of water have not been sufficiently addressed, Raymond says atrazine can be banned as a weed control tool for farmers. Some watersheds across the country, where atrazine residue levels in drinking water have exceeded EPA levels of concern, currently are at risk for that decision, she says.

However, in the majority of cases where farmers have proactively implemented BMPs, good results have followed.

“We'll continue to have access to atrazine if we work with EPA and other entities to address concerns about atrazine use, as long as growers continue to use these products judiciously,” Martin says. “With fewer new active ingredients in development, we need to protect established products so they're still viable and available for use in the future.”